The present invention relates to packaging plant tissues cultured in vitro so that the tissues packages are preserved in the package, particularly for and during transport of the tissues.
The transport of plant tissues cultured in vitro requires an appropriate packaging. For example, plant tissues may be packaged by placing them in a liquid culture medium or on a semi-solid agar medium, these media being contained in customary containers for in vitro culture, such as Petri dishes or bottles. Unfortunately, this type of packaging does not correspond to the dangers to which a packet may be subjected during transport, namely, (1) asphyxiation of the tissues by a lack of agitation in the case of liquid cultures; (2) a covering of the tissues with agar due to excessive shakings which will cause asphyxiation of the tissues; (3) contaminations resulting from contact between the culture media and the outside of the containers; and (4) excessive growth of the tissues in the case of some species.
It is also possible to package plant tissues cultured in vitro under a layer of oil at refrigeration temperatures. European Patent Application Publication No. 0 408 922 describes a process in which embryos are kept in hypoxia by immersion under a layer of oil and are cooled and preserved at a temperature greater than the cold sensitivity threshold of the embryos considered. Although the embryos thus preserved exhibit a satisfactory viability after a few days of preservation, this method is still subject to the hazards of changes in refrigeration temperatures during transport.
It is also possible to transport plant tissues cultured in vitro when they are coated with a mixture of alginate and sucrose (Hasan et al., Plant Genetic Resources Newsletter, 103, 32-35, 1995).
It is also possible to freeze tissues of plants cultured in vitro. By way of example, Chen et al. propose culturing calli in the presence of sorbitol (dehydrating agent) and dimethyl sulphoxide (cryoprotectant), freezing them slowly at -40.degree. C. and then in liquid nitrogen (Plant Physiol., 75, 726-731, 1984). Likewise, Delvallee et al. propose culturing immature zygotic embryos in the presence of sucrose (dehydrating agent) and dimethyl sulphoxide, and then freezing them in liquid nitrogen (Plant Science, 60, 129-136, 1989). Finally, European Patent Application Publication No. 0 399 158 describes a process in which somatic embryos are pretreated on a medium comprising an osmotic pressure agent, and then they are cooled and they are frozen at a temperature of between -15.degree. C. and -40.degree. C. Unfortunately, freezing is not always suited to the transport of plant tissues because of the temperature hazards which may lead to the death of the tissues.
Moreover, in a different technical field, methods for preserving plant cuttings or seeds are known. European Patent Application Publication No. 66 581 proposes, for example, a device for causing seeds to germinate or for preserving plant cuttings, which consists of a container in which the biological material is placed between a first adhesive support and a second supple support which can be impregnated with liquid components, both supports being kept firmly attached by the adhesive surface of the first support, and the two supports being kept on the sides of the container by means of adhesives. It may be noted that this device is not sterilizable because of the presence of adhesives. Furthermore, the adhesive surface of the first support is capable of damaging soft tissues, such as plant tissues cultured in vitro, which further limits the attraction of this device within the framework of the present invention.
So far, no device for packaging plant tissues cultured in vitro is therefore known which is both simple to use and which can satisfactorily protect the plant tissues.